In surgical retinopexy performed as a remedy for retinal detachment, proliferative vitreoretinopathy, a disease associated with excessive proliferation of retinal pigment epithelial cells, is known to remain as a cause of worsening prognosis. At the present time, only vitreous surgery has been used as a remedy for such proliferative vitreoretinopathy. Under present conditions, visual prognosis is not necessarily said to be favorable even after the surgery. It is well known that the proliferation of retinal pigment epithelial cells plays an important role in the occurrence and development of such proliferative vitreoretinopathy. Many researchers have studied the inhibitory effects of various drugs on proliferation of retinal pigment epithelial cells (Japanese Review of Clinical Ophthalmology, Vol. 9, pp. 1886-1890 (1993); Japanese Review of Clinical Ophthalmology, Vol. 9, pp. 2030-2034 (1993).
On the other hand, the technical progress of vitreous surgery has resulted in remarkable improvements in the cure rate of retinal detachment. However, a limit of the cure rate is said to be 92-94%. It is thought that proliferative vitreoretinopathy, namely, proliferation of retinal pigment epithelial cells largely participates as the cause of limiting the cure rate. Therefore, development of drugs having excellent inhibitory effects on excessive proliferation or retinal pigment epithelial cells have been desired to improve the cure rate of retinopexy for retinal detachment and for the prevention or treatment of proliferative vitreoretinopathy.
Tranilast has been used widely as a drug for the treatment of allergic disorders such as bronchial asthma, allergic rhinitis, atopic dermatitis and allergic conjunctivitis, and cutaneous disorders such as keloid and hypertrophic scar. For example, it has been known that Tranilast has inhibitory effects on chemical mediator release caused by an allergic reaction, excessive collagen accumulation by fibroblast cells in cutaneous tissues and excessive proliferation of smooth muscle cells in coronary artery vessels.
However, it has not been disclosed that Tranilast suppresses proliferation of retinal pigment epithelial cells and is therefore useful as an agent for the prevention or treatment of proliferative vitreoretinopathy.